The present invention concerns a method for suppressing mutual interference between two or more active radar systems operating in close proximity or formation.
Mutual interference (MI) between adjacent active defensive or offensive radar systems in military aircraft, can significantly affect the performance of each such radar system when both are emitting in a formation. The two major performance problems are false alarms and degraded system sensitivity. False alarms must be controlled by blanking to handle the worse case variable interference levels when the interfering radars are not operating at the same Pulse Repetition Frequency (PRF) and the signal levels exceed detection thresholds. Such interference levels vary with both separation range and frequency but the doppler MI frequency patterns can be uniquely recognized and detected. Digital blanking techniques which also detect opposite PRF MI have in fact been designed to blank such interference on a "coherent look basis," for the range gates and doppler filters affected by mutual interference.
The effect of mutual interference on system sensitivity, however, is a separate consideration. This is especially true for defensive missile warning radars requiring simultaneous operation over long time periods. While pulse shaping of the rise and fall time characteristics of the received radar reduces the sensitivity loss, this technique alone is not a practical solution for close formations with separations less than 0.5 NMI. However with the following adaptive MI suppression technique, the detection sensitivity loss will be minimized over the time intervals of opposite (or different for 3 or more PRF's) PRF blanking.